i would like to install XAMPP on my Kubuntu 15 system...in fact on a USB drive...so by default not on /opt/xampp.however from basic run i see nowhere such possibility.

so is there any option to install somewhere else ?thx.

You either may mount the USB stick to /opt/lampp and/or move to /opt/lampp to any location, but there MUST BE an /opt/lampp folder, on linux you can create a symbolic link from the Xampp folder to /opt/lampp. So it is physically stored on the stick, but /opt/lampp still resolves to that stick.